GraphMLSerializer does not serialize derived vertex/edge attributes

[leryss]

Seems the serializer just looks at the base type of the vertex for attribute serialization. Is this by design ?

QuickGraph/src/QuickGraph/Serialization/GraphMLSerializer.cs

Lines 452 to 455 in 50e0e16

	string forNode = "node";
	Type nodeType = typeof(TVertex);
	this.WriteAttributeDefinitions(forNode, nodeType);